1. Field of the Invention
The present invention relates to a boost circuit configured to boost the amplitude of a bitstream signal.
2. Description of the Related Art
Delta-sigma modulators configured to convert an analog voltage into a digital bitstream signal are known. FIG. 1 is a block diagram which shows a configuration of a typical primary delta-sigma modulator 300. The delta-sigma modulator 300 performs delta-sigma modulation on an analog input signal Vin so as to convert the analog input signal Vin into a digital bitstream signal Dout.
A boost circuit 308 boosts the amplitude of the bitstream signal Dout approximately twofold, for example. A digital/analog conversion circuit (DAC) 310 is a 1-bit DAC, which judges whether the bitstream signal Dout′ thus boosted is low level or high level. When the bitstream signal Dout′ is high level, the digital/analog conversion circuit 310 outputs a feedback signal Vfb at a reference voltage Vref1, and when the bitstream signal Dout′ is low level, the digital/analog conversion circuit 310 outputs a feedback signal Vfb at a reference voltage Vref2. An adder 302 generates a difference voltage Vdiff, which is obtained by subtracting the feedback voltage Vfb from the input voltage Vin. An integrator 304 integrates the difference voltage Vdiff. An analog/digital conversion circuit (ADC) 306 converts the output signal Vint of the integrator 304 into a binary bitstream signal Dout.